Degradation phenomena in small-molecule organic light-emitting devices

Studies of electroluminescence degradation mechanisms in small-molecule-based organic light-emitting devices (OLEDs) are reviewed. Luminescence degradation due to the growth of visible nonemissive defects, widely referred to as dark spots, as well as device catastrophic failure phenomena are addressed briefly. A special emphasis is given to intrinsic degradation phenomena that cause the decrease in the electroluminescence efficiency of the OLEDs during operation. In the discussion of intrinsic degradation, some widely accepted models that have been proposed to explain the degradation behavior are introduced and reviewed in view of experimental observations. These models are (i) the morphological instability model, (ii) the unstable cationic AlQ(3) model, (iii) the indium migration model, (iv) the mobile ionic impurities model, and (v) the immobile positive charge accumulation model.